For the first time in 12 years, Anne Arundel County's most powerful Democratic official may face an election-year challenge -- from an unexpected source.

County Council Chairman C. Edward Middlebrooks, a registered Democrat, said he is considering a bid to unseat state Sen. Michael J. Wagner, a three-term incumbent, and might switch parties this week to better his chances.

"It's about time people are given a serious alternative to the Wagner machine," said Mr. Middlebrooks, 38, of Old Mill. "I can't remember the last time the senator has had to debate the issues of importance to our constituents."

Mr. Wagner, 52, a Ferndale caterer, has been considered unbeatable. He last faced opposition in the 1982 primary, when he defeated Victor Sulin, then a neophyte and now a state delegate. He has never faced a Republican in a general election.

Mr. Middlebrooks, a former member of the Democratic Central Committee, the party's ruling body, said he has not changed party loyalties but has been courted by some GOP officials. He said he might make the change even if he does not run against Mr. Wagner.

"The Wagner organization is an entrenched, good-old-boy system that I'm never going to fit into, no matter what I run for," he said. "It ain't just that [Glen Burnie] area. He plays granddaddy for the whole county."

Mr. Middlebrooks said a change of party affiliation could help him in a Senate bid, especially by allowing him to bypass the Democratic primary and allowing him to appeal to wider range of voters. He said he has been analyzing voter demographics to determine whether he would still be viewed as a credible candidate as a Republican.

John Greiber, who is part of a GOP committee recruiting candidates to challenge Democrats in every county race, said yesterday that he was confident Mr. Middlebrooks would switch. He said he took notice of Mr. Middlebrooks after the councilman withdrew from the county's lucrative and controversial pension plan.

Mr. Greiber said the GOP has not specifically courted Mr. Middlebrooks to challenge Mr. Wagner for the Senate seat in District 32, which includes Linthicum, Glen Burnie and Maryland City.

Unfettered by opponents challenging him for his seat, Mr. Wagner has become a potent fund-raiser, organizer and campaigner for Democrats throughout the county. If he had no opponents again this year, his campaign organization could play a large role in who becomes the next county executive and in other countywide races, such as sheriff, state's attorney and clerk of the court.

"He's definitely a key player," said state Sen. Philip C. Jimeno, a Brooklyn Park Democrat.

Mr. Jimeno worries that if Mr. Middlebrooks remains a Democrat, a fractious primary between Mr. Wagner and Mr. Middlebrooks could undermine his party's chances. Mr. Jimeno said he would support Mr. Middlebrooks' re-election to the council because of his efforts to get money for North County High School and his opposition to a new county jail on Ordnance Road.

However, in a test of loyalties, Mr. Wagner wins. "Since I first ran for Senate in '86, Mike has always been in my corner," Mr. Jimeno said. "I have to remain loyal to Mike."

Others suggest that a potent Republican challenger would do more damage, forcing Mr. Wagner to spend more time defending his own turf instead of helping other Democrats.

Mr. Wagner and other party officials doubt that Mr. Middlebrooks will run for the Senate. Most expect him to seek re-election to the council, which he announced he would do last fall, or to seek a seat in the state House of Delegates.

"Senator Wagner has a tremendous amount of support in the district. Even his enemies love him," said Daryl D. Jones, a member of the county Democratic Central Committee and a former Glen Burnie resident. "Certainly, Eddie has to take that into consideration."

Mr. Middlebrooks also must consider a challenge to his council seat from James "Ed" DeGrange, a Glen Burnie businessman whom Mr. Wagner encouraged to run last fall in the Democratic primary.

Mr. DeGrange enjoys wide recognition in the community for a first-time candidate because his family has operated a hardware store on Ritchie Highway for years. But his place on Mr. Wagner's ticket makes him a particularly formidable opponent for Mr. Middlebrooks.

"Eddie is in store for a very tight race" if he runs for council, Mr. Jones said. "He's probably assessing if it's worth the energy or if he should try to move on to higher office. It's very possible he's posturing himself to make a run for House of Delegates."

Mr. Wagner and Mr. Middlebrooks have had a long-running feud, each accusing the other of failing to adequately represent the Glen Burnie area. Mr. Wagner also clearly links Mr. Middlebrooks to H. Erle Schafer, a former Glen Burnie senator and Mr. Wagner's political nemesis.

Mr. Schafer, a friend of Mr. Middlebrooks', was the last man to beat Mr. Wagner at the polls. A state delegate who was first appointed to a vacant Senate seat in 1977, Mr. Wagner lost a bitter primary battle to Mr. Schafer, a former councilman, in 1978.

Asked why he recruited Mr. DeGrange, Mr. Wagner describes Mr. Middlebrooks as someone who does not work well with other elected representatives, overemphasizes regional divisions between North and South County residents and plays to the news media.

"I guess I'm not that excited about the Erle Schafers and Ed Middlebrooks out there who are splashy while the cameras are there and then do nothing," Mr. Wagner said.

Mr. Middlebrooks portrays Mr. Wagner as a back room politician more interested in keeping the county executive and governor happy than in his own constituents.

"That's why he didn't come out strongly against the jail," said Mr. Middlebrooks, referring to County Executive Robert R. Neall's proposal to build a county jail on Ordnance Road in Glen Burnie.

Although the senator voted against state financing of the jail's design, "he sat on his hands and did nothing" to stop the jail in the three years since it was first proposed, Mr. Middlebrooks said.

But if that is his chief issue, Mr. Middlebrooks may not have much of a platform. The proposed jail would be in District 31, which is represented by Mr. Jimeno, who vigorously opposed it.

"I don't see it as being a make-or-break issue in District 32," Mr. Jones said.